Pop Using Linked List Node in DSA Go

Introduction

Syntax

Examples

Sample Program

Important Notes

Summary

Practice

1. What does the pop operation do in a linked list when implemented using nodes?

easy

A. Counts the total number of nodes

B. Adds a new node at the end

C. Removes the first node and returns its value

D. Searches for a node with a specific value

Solution

1. Step 1: Understand pop operation in linked list

   Pop means removing the top or first element from the list.

2. Step 2: Identify what happens to the first node

   The first node is removed and its value is returned, updating the head pointer.

3. Final Answer:

   Removes the first node and returns its value -> Option C

4. Quick Check:

   Pop = Remove first node [OK]

Hint: Pop always removes the first node in a linked list [OK]

Common Mistakes:

• Thinking pop adds nodes instead of removing
• Confusing pop with search or count operations
• Removing the last node instead of the first

2. Which of the following is the correct Go syntax to define a node struct for a singly linked list?

easy

A. class Node { int value; Node next; }

B. struct Node { int value; Node* next; }

C. Node := struct { value int; next Node }

D. type Node struct { value int; next *Node }

Solution

1. Step 1: Recall Go struct syntax

   In Go, structs are defined with 'type Name struct { fields }'.

2. Step 2: Check pointer usage for next node

   The next field must be a pointer to Node: '*Node'.

3. Final Answer:

   type Node struct { value int; next *Node } -> Option D

4. Quick Check:

   Go struct with pointer = type Node struct { value int; next *Node } [OK]

Hint: Use 'type' and pointers for linked list nodes in Go [OK]

Common Mistakes:

• Using C/C++ or Java syntax in Go
• Missing pointer '*' for next node
• Trying to declare struct inline incorrectly

3. What will be the output after popping once from the linked list represented by nodes with values 10 -> 20 -> 30 -> null?

medium

A. 20 -> 30 -> null

B. 10 -> 20 -> 30 -> null

C. 30 -> null

D. null

Solution

1. Step 1: Identify the first node value

   The first node has value 10.

2. Step 2: Remove first node and update head

   After popping, head points to node with value 20, so list is 20 -> 30 -> null.

3. Final Answer:

   20 -> 30 -> null -> Option A

4. Quick Check:

   Pop removes 10, new head 20 [OK]

Hint: Pop removes first node, so list starts from second node [OK]

Common Mistakes:

• Not updating head pointer after pop
• Returning the whole list instead of updated list
• Confusing pop with removing last node

4. Given this Go code snippet for pop operation, what is the error?

func pop(head *Node) (*Node, int) {
    if head == nil {
        return nil, 0
    }
    value := head.value
    head = head.next
    return head, value
}

medium

A. It returns wrong value from the node

B. The function does not update the original head pointer outside

C. It causes a runtime panic due to nil dereference

D. The function should return only the value, not the new head

Solution

1. Step 1: Understand pointer behavior in Go

   Assigning 'head = head.next' changes local copy, not original head outside.

2. Step 2: Identify missing pointer update

   The original head pointer outside the function remains unchanged, so pop has no effect.

3. Final Answer:

   The function does not update the original head pointer outside -> Option B

4. Quick Check:

   Local pointer change doesn't affect caller [OK]

Hint: Update original pointer by returning new head or using double pointer [OK]

Common Mistakes:

• Assuming local pointer change updates original
• Ignoring need to return new head
• Not checking for nil before accessing value

5. You have a linked list with nodes 5 -> 15 -> 25 -> 35 -> null. You pop twice and then add a new node with value 45 at the front. What is the final list?

hard

A. 45 -> 25 -> 35 -> null

B. 25 -> 35 -> 45 -> null

C. 45 -> 35 -> null

D. 15 -> 25 -> 35 -> 45 -> null

Solution

1. Step 1: Pop twice from the list

   First pop removes 5, list becomes 15 -> 25 -> 35 -> null. Second pop removes 15, list becomes 25 -> 35 -> null.

2. Step 2: Add new node with value 45 at front

   New node 45 points to current head 25, so list is 45 -> 25 -> 35 -> null.

3. Final Answer:

   45 -> 25 -> 35 -> null -> Option A

4. Quick Check:

   Pop twice then add front = 45 -> 25 -> 35 [OK]

Hint: Pop removes from front; adding front inserts new head [OK]

Common Mistakes:

• Not updating head after each pop
• Adding new node at end instead of front
• Confusing order of operations